This invention relates to certain polyvinyl chloride compositions having improved properties and processability consisting essentially of blends of polyvinyl chloride with plasticizers which are members of a class of defined terpolymers.
It is known in the art to add plasticizers to polyvinyl chloride (PVC) to improve its flexibility. Although various plasticizers have been used in such applications, certain ethylene terpolymers of the general formula E/X/CO, where E is ethylene, and X is a "softening" monomer such as, for example, vinyl acetate or an acrylic ester, have been found to be particularly suitable for this purpose. Such terpolymers and their use as plasticizers for PVC e described in U.S. Pat. No. 3,780,140 to Hammer. Because of their polymeric nature, these materials do not have the tendency, exhibited by conventional aromatic ester type plasticizers, of exuding or evaporating with time from PVC, which would make PVC brittle and unsuitable for many applications. These polymeric plasticizers have the additional advantage that they are completely compatible with PVC within rather broad composition ranges. Terpolymers having the same general structure, but with the SO.sub.2 group replacing the CO group, have been disclosed in U.S. Pat. No. 3,684,778 to Hammer and are suitable for the same purpose.
When the softening monomer in the terpolymer is vinyl acetate, calendered sheets of PVC blends with such a terpolymer are generally satisfactory. However, such terpolymers are less thermally stable than when the softening monomer in the terpolymer is an acrylic acid ester, so that PVC blends with a terpolymer containing an acrylic acid ester comonomer would be more desirable. Nevertheless, calendered sheets made of PVC plasticized with acrylic acid ester-containing terpolymers described in the above two patents generally are rough, rather than smooth. This means that those blends have "high nerve".
It would be desirable, therefore, to be able to plasticize PVC in a manner which would permit the plasticized polymer to be calendered into smooth sheets.